jack-play: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/jack-play - from package: jack-tools

You may install the required package with command apt-get install {package}

Error in other languages:
jack-play: bevel nie gevind nie
jack-play: comandă negăsită
jack-play: comando não encontrado
jack-play: commande introuvable
jack-play: command not found
jack-play: käsku ei ole
jack-play: không tìm thấy lệnh
jack-play: komanda nerasta
jack-play: Kommando nicht gefunden.
jack-play: kommandot finns inte
jack-play: komut yok
jack-play: nie znaleziono polecenia
jack-play: níor aimsíodh an t-ordú
jack-play: no se encontró la orden
jack-play: no s'ha trobat l'ordre
jack-play: opdracht niet gevonden
jack-play: parancs nem található
jack-play: perintah tidak ditemukan
jack-play: príkaz nenájdený
jack-play: příkaz nenalezen
jack-play: команда не найдена
jack-play: командата не е открита
jack-play: 命令找不到
jack-play: コマンドが見つかりません